Multiple source alignment sensor with improved optics

ABSTRACT

Features of the present invention provide an optical layout that can accommodate the relatively strict enclosure requirements for compact component alignment sensor. Specifically, aspects of the present invention provide a single optical component that reduces the degree of divergence, and preferably substantially collimates light from the plurality of divergent light sources prior to entering the sensing field. In this regard, part count is kept low and the physical size of the optical train itself is relatively small.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-part Application of U.S. patentapplication Ser. No. 09/767,199 filed Jan. 22, 2001 now U.S. Pat. No.6,762,847 entitled Laser Align Sensor with Sequencing Light Sources; Theapplication is also a non-provisional application of, and claimspriority to, U.S. Provisional Application Ser. No. 60/406,822, filedAug. 29, 2002 and entitled Multiple Source Laser Align Sensor withImproved Optics.

BACKGROUND OF THE INVENTION

The present invention relates to control systems which align electricalcomponents for precise placement via pick-and-place machines ontosurfaces such as printed circuit boards, hybrid substrates containingcircuitry traces, and other carriers of circuit tracings. Morespecifically, the present invention relates to a non-contact light-basedsensor system which precisely determines angular orientation andlocation (x, y) of components to allow a pick and place machine tocorrect angular orientation of the component with respect to the pickand place machine's coordinate system for proper placement.

The electronic device assembly industry uses pick and place machines toautomatically “pick” components from standardized feeder mechanisms,such as tape reels, and “place” such components upon appropriatecarriers such as printed circuit boards. A given printed circuit boardmay include a large number of such components and thus the automation ofcomponent placement upon the printed circuit board is essential for costeffective manufacture. One important aspect of a given pick and placemachine is the manner in which component orientation and location aredetected prior to placement. Some pick and place machines transport thecomponent to an inspection station where it is imaged by an inspectioncamera, or the like (i.e. off-head systems). Once imaged, thecontroller, or other appropriate device, calculates orientation andlocation information from the component image. One drawback associatedwith such systems is the added time required to transport the componentto the imaging station; to image the component; and to transport thecomponent from the imaging station to the placement location. Anothertype of pick and place machine uses an “on-head” sensor to essentiallyimage the component while being transported from the component feeder tothe placement location. Thus, in contrast to the above example, on-headcomponent inspection systems typically allow higher component throughputand thus lower cost manufacture.

Pick and place machines that incorporate on-head sensors are known. Onesuch device is taught in U.S. Pat. No. 5,278,634 issued to Skunes etal., and assigned to the assignee of the present invention. U.S. Pat.No. 5,278,634 discloses an on-head component detector that uses a singlelight source to direct illumination at and past a component of interest,which illumination then falls upon a detector. The component fitsthrough a fixed size window in the housing of the Skunes '634 sensor.With the light energized, the component is rotated by a vacuum quillwhile the width of the shadow cast upon the detector is monitored. Theminimum shadow width is registered when the sides of a rectangularcomponent are aligned normally with respect to the detector. Associatedelectronics, sometimes resident in the pick-and-place machine, computethe desired rotational movement of the nozzle (with knowledge ofreference axes of the pick-and-place machine). This allows angularorientation of the component, as well as component position to bedetermined, and corrected for proper placement.

Other pick-and-place machines employ sensors with multiple light sourcesin the sensor, to accommodate components of varying sizes.

Although the system taught by Skunes et al. has provided a significantadvance to the art of electronic component placement in pick and placemachines, an efficient sensor adapted for use with components having awide range of sizes would provide faster placement and less machinedown-time to exchange sensors with different sized windows.

SUMMARY OF THE INVENTION

Features of the present invention provide an optical layout that canaccommodate the relatively strict enclosure requirements for compactcomponent alignment sensor. Specifically, aspects of the presentinvention provide a single optical component that reduces the degree ofdivergence, and preferably substantially collimates light from theplurality of divergent light sources prior to entering the sensingfield. In this regard, part count is kept low and the physical size ofthe optical train itself is relatively small.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top plan view of a pick and place machine of the presentinvention.

FIG. 1B is a perspective drawing of a sensor of the present invention.

FIG. 2 is a diagrammatic view of a system for detecting componentorientation and location in accordance with an embodiment of the presentinvention.

FIG. 3 is a diagrammatic view of a system for detecting componentorientation and location in accordance with another embodiment of thepresent invention.

FIG. 4 is a diagrammatic view of a system for detecting componentorientation and location in accordance with another embodiment of thepresent invention.

FIG. 5 is a diagrammatic view of a system for detecting componentorientation and location in accordance with another embodiment of thepresent invention.

FIG. 6 is a diagrammatic view of a system for detecting componentorientation and location in accordance with another embodiment of thepresent invention.

FIG. 7 is a diagrammatic view of a system for detecting componentorientation and location in accordance with an embodiment of the presentinvention.

FIG. 8 is a diagrammatic view of a single detector source pair.

FIG. 9 is a diagrammatic view of a system for detecting componentorientation and location in accordance with an embodiment of the presentinvention.

For convenience, items in different figures having the same referencedesignator number are the same, or serve the same or similar function,as appropriate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a top plan view of pick and place machine 150 for whichembodiments of the present invention are particularly useful. Althoughthe description of FIG. 1A will be provided with respect to pick andplace machine 150, other forms of pick and place machines such as splitgantry designs, can be used. As illustrated in FIG. 1A, machine 150includes transport mechanism 152 that is adapted to transport aworkpiece such as a printed circuit board. Transport mechanism 152includes mounting section 154 and conveyor 156. Transport mechanism 152is disposed on base 158 such that the workpiece is carried to mountingsection 154 by conveyor 156. Feeder mechanisms 160 are generallydisposed on either side of transport mechanism 152 and supply electroniccomponents thereto. Feeders 160 can be any suitable devices adapted toprovide electronic components.

Pick and place machine 150 includes head 162 disposed above base 158.Head 162 is moveable between either of feeder mechanisms 160 andmounting section 154. As can be seen, head supports 164 are moveable onrails 166 thereby allowing head 162 to move in the y direction over base158. Movement of head 162 in the y direction occurs when motor 170, inresponse to a motor actuation signal, rotates ball screws 172 whichengages one of head supports 164 to thereby displace the support 164 inthe y direction. Head 162 is also supported upon rail 168 to allow headmovement in the x direction relative to base 158. Movement of head 162in the x direction occurs when motor 174, in response to a motoractuation signal, rotates ball screw 176, which engages head 162 anddisplaces head 162 in the x direction. Other pick-and-place designs,even those which do not operate exclusively in x and y movements, may beadapted for use with the present invention.

Head 162 generally includes body 178, nozzle mount 180, nozzles 182, andsensor 184. Nozzle mount 180 is disposed within body 178 and mounts eachof nozzles 182 within body 178. As used herein, “nozzle” is intended tomean any apparatus capable of releasably holding a component. Each ofnozzles 182 is movable in the z direction (up/down), x and y directions,and is rotatable about the z axis by any suitable actuation members,such as servo motors. Sensor 184 is adapted to acquire shadowinformation related to components held by nozzles 182. Sensor 184includes suitable illumination devices and detection devices such thatsensor 184 can provide shadow information that varies based uponcomponent orientation and off-set. Sensor 184 can be mounted on head162, or alternatively sensor 184 can be mounted at a fixed location withrespect to head 162. The information provided by sensor 184 toprocessing electronics 34 is used to calculate respective componentorientations and offsets. Such information includes calculating offsetin the x and y axes as well as rotational offset.

FIG. 1B shows sensor 184 separately, with sources 12, 14, 15.Component(s) fit partially within sensing field 31, and obscureillumination from each of the successively energized sources as it fallsonto a detector 24. Electronics 26 receive a plurality of outputs fromthe detector as a nozzle (not shown) rotates the component. Electronics26 may be partially located outside of sensor 184 in a pick-and-placemachine.

FIG. 2 is a diagrammatic view of component orientation and placementdetection system 10 in accordance with an embodiment of the presentinvention. System 10 includes sources 12, 14 which are arranged todirect illumination 16 upon component 18 from at least two differentangles. Sources 12, 14 can be any suitable light sources as long as theyprovide illumination of sufficient intensity, as considered from eachsource. Thus, sources 12, 14 can be sources incoherent or coherentillumination. Preferably, sources 12, 14 are laser diodes, but in someembodiments, sources 12, 14 are light emitting diodes (LED's). Sources12, 14 can be positioned to provide illumination in substantially thesame plane, as defined by either of the sources and two points on thedetector (a beginning and an ending pixel on the detector). Although apair of sources 12, 14 are shown, any suitable number of sources, suchas three sources, can be used. Illumination 16 from sources 12, 14 isblocked, to some extent, by component 18 to thereby generate shadows 20,22, respectively, on detector 24 which is preferably a linear chargecoupled device (CCD) sensor or a Complementary Metal Oxide Semiconductor(CMOS) sensor. Detector 24 includes a number of photoelectric elements,or pixels. Detector 24 essentially captures shadows 20, 22 in a briefinstant of time and provides data (e.g. detector output) related to thecaptured shadow image to detector electronics 26 via link 28. Asdesired, additional optical components (e.g. lenses, prisms, etc.) maybe placed in front of the detector 24 so that the image of the component(the imaged or focused shadow) is incident upon detector 24, which thenprovides detector output representative of the shadow image rather thanthe shadow. As used herein, “shadow” is intended to mean anyrepresentation that is generated in part by light of intensity thatvaries based upon at least partial obstruction by a component ofinterest. Thus, a shadow may or may not be focussed before falling upona detector.

As component 18 is held, or otherwise affixed to nozzle 30, component 18is rotated as indicated by arrow 32 while sources 12, 14 are selectivelyenergized. As can be appreciated, during rotation of part 18, shadows20, 22 will change size and position based upon the cross sectional areaof component 18 obstructing a given beam 16 of illumination. The signalfrom detector 24 is read, and/or stored during rotation of component 18such that data from detector 24 is used to compute rotationalorientation of component 18 as well as location (x, y) of component 18with respect to nozzle 30. Detector electronics 26 provides this data toprocessing electronics 34 via link 36. As illustrated in FIG. 2,processing electronics 34 is also preferably coupled to source controlelectronics 38 such that processing electronics 34 controls energizationof sources 12, 14 during rotation of component 18. Source controlelectronics 38, or energization electronics 38, is mounted within sensor184 in some embodiments. Processing electronics 34 can reside within asuitable personal computer and includes appropriate software forcomputing angular orientation and offset. Processing electronics 34 isalso coupled to encoder 40 such that processing electronics 34 isprovided with a signal from encoder 40 that is indicative of angularorientation of nozzle 30. Thus, by essentially knowing which sources areenergized, knowing the angular orientation of nozzle 30 as indicated byencoder 40, and by detecting images of the shadows cast by component 30while rotated, processing electronics 34 computes component orientationand location, given suitable knowledge of the internal geometry of thesensor.

FIG. 2 shows a double-edged measurement, as considered with respect toeither of sources 12, 14, since shadows of two edges of component 18fall on detector 24.

Various embodiments of the present invention are designed to be able toextract component information (part size, center offset, and angularorientation, etc.) using either single edge or double edge measurementsof the component under inspection. Typically, double edge measurementsare used when the dimensions of the component allow the shadows of bothcomponent edges to fall upon the detector during the same componentmeasurement time, without overlapping, as illustrated in FIG. 2. Thus,at least two edges of the component can be shadowed onto the detector bydifferent sources within the same component measurement time. Thedifference between single edge measurement and double edge measurementis that during the single edge measurement process, only one edge of thecomponent is shadowed by any source onto the detector due to thecomponent being so large that the shadow of the other edge of thecomponent would not fall on the detector.

Two or more sources are sequenced to reduce elapsed time before imageinformation is collected for computation. This is particularlyadvantageous when these sources are spaced separately with respect tothe plane that is defined by the sources, and the CCD or imaging array(see, for example, FIG. 1B). Since the sources are generally atdiffering angular positions from each other relative to a line drawnfrom nozzle 30 normal to the surface of detector 24, each of sources 12,14 will have its principal ray directed at a different angle withrespect to this normal line as incident onto component 18. As usedherein, the principal ray is that ray emanating from the center of theillumination generated by the radiation source, nominally referencedfrom the mechanical axis of the detector body, such that the core ofemanated radiation, (which is typically symmetrical) is bisected by theprincipal ray. This allows the information included in the shadow, suchas edge information, to represent a different spatial position of thecomponent, i.e. the edge of one side may be lined up with respect to thesource 12 and, in less than 90 degrees of component rotation anotherside may be lined up with respect to source 14, as illustrated in FIG.2.

The light sources 12, 14 are sequenced in any suitable manner. Forexample, sequencing sources 12, 14 at the full frame readout rate ofdetector 24 (e.g. 2 kHz line read-out rate), reduces the amount of timethat elapses between these sources being sequenced such that the amountof angular rotation of the component during that interval is relativelysmall. By sequencing the sources so, shadow images derived from eithersource individually can be obtained such that the movement of thecomponent between any particular shadow image can be reduced, thusreducing the granularity and enhancing the resolution of the sequence ofimages from that particular source. Each source allows collection ofshadow images from a different rotational position of the component.Based on the different source locations with respect to the component,shadow images from more than one angular position of the component arecollected within a relatively small time. The component information canbe collected in less time than would be required if a single source,were energized to collect the data since full rotation of the componentwould be required in order to obtain the angular information.

Another important feature of embodiments of the present invention is theability to create a measurement envelope, or sensing field of varyingdimension. As used herein, a “sensing field” is a cumulative spaceilluminated by the energized sources in the sensor (when all sources areenergized), as modified by any mechanical obstruction such as a housing.Thus, a sensing field need not even require a mechanical housing. Thesensing field is formed by accommodating a plurality of sourcespositioned such that a single sensor can sense orientation forcomponents of varying size. For example, if a component is 25millimeters from side-to-side then one energized source, placed 12.5millimeters from the nominal center of the component and disposed normalto the detector with its principal ray, would capture the edge of thecomponent that was rotating in the sensing field. This embodiment, inits simplest form, requires only one energized source per componentsize. The sources have a specified solid cone angle of light emittedfrom them so the distance from the nominal center and lateral or roughlyparallel to, the detector surface as discussed above can be adjusted toaccount for this divergence of the source light in order to cast ashadow of the edge of the part. However, a source that is placed withits principal ray pointing at, for example, an 8 millimeter positionfrom nozzle 30 and along the diameter of the component 18 parallel todetector 24 would be blocked, depending on the relative orientation ofthe solid angle of light as well as the position of the source. Basedupon the solid angle of each source 12, 14, and the component size, eachsource will illuminate various sections of the component. It isimportant to select which one or more of the plurality of sources toenergize, since differently sized components mandate the use ofdifferent sources to generate even a portion of a shadow. Source controlelectronics 38 can also provide selective source energization based uponanticipated component size. However, source control electronics canprovide varying energization sequences for components of the same sizein order to expedite processing, or provide additional information aboutthe components.

As components are exchanged from small to larger parts in the samesensor, sources having principal rays that are pointed increasinglyfurther along a line parallel to, or lateral from, detector 24, butmeasured from a line normal to detector 24, through nozzle 30 or thecenter of rotation of the component will image increasingly largecomponents' edges by selectively sequencing sources 12, 14. (See arrow Ain FIG. 1B). Preferably, sources 12, 14 are sequenced to cast shadowsfrom opposite sides of component 18 in the same component measurementtime interval (in the case where each source casts a shadow of a side).Selection of an appropriate source allows the source, generally based ona priori knowledge of expected part size, to be turned on such that anedge of component 18 can be imaged onto the detector 24. This allowscomponents of varying sizes to be imaged on detector 24 withoutrequiring the use of multiple sensors that are of a fixed measurementenvelope, or sensing field.

Although the description above has focused on embodiments where a singlenozzle is disposed within the sensing field, other embodiments canprovide any suitable number of nozzles in the sensing field. FIG. 3 is adiagrammatic view of system 20 for detecting component orientations inaccordance with another embodiment of the present invention. System 20includes many of the same or similar elements as system 10 shown in FIG.2 and like elements are numbered similarly. FIG. 3 illustrates that morethan one nozzle 30 can be disposed in the sensing field 31, such thatmultiple component orientations and the locations can be imagedsubstantially simultaneously in order to reduce processing time.

The sensing field 31 is the area between the radiation (light) sources,and the detector, where components placed upon the nozzles will havelight directed upon them. In this embodiment, shadows from thecomponents' edges are cast upon detector 24. Depending upon thelocations of nozzles 30 and sources 12, 14, a particularly sizedcomponent 18 is measured by sequencing the various sources 12, 14, etc.such that shadows of the component 18 can be distinguished from shadowsof components on other nozzles. Source 12, 14 time sequencing is shownin FIG. 3 where electronics 38 energizes source 12 first, and thenenergizes source 14. This has an advantage of allowing more than onecomponent 18 to be measured in the sensing area at essentially the sametime. Further, depending upon the spacing of nozzles 30, the nozzles canhold components of varying sizes, yet still allow measurement of thecomponent to be accomplished while such components are rotated on thenozzles.

FIG. 3 is an example of a double edged measurement, as considered withrespect to sources 12, 14, since shadows of the two edges of component18 fall on detector 24.

FIG. 4 is a diagrammatic view of component measurement system 50 inaccordance with another embodiment of the present invention. FIG. 4illustrates a sensing field 31 where detector 24 comprises twospaced-apart detector portions 24A, 24B, each one of which receiveslight incident from a specific source 12, 14. Detector portions 24A and24B can be disposed adjacent to one another at a variety of angles,since each source detector pair operates independently. The principalaxis of detector 24A need not be in the same plane as the principal axisof detector 24B. Moreover, detector portions 24A and 24B can be arrangedto image shadows from different parts of the component. Using separatedetector portions allows for the use of smaller detector portions, and,if necessary, allows the detector portions 24A, 24B to be packagedseparately. In this manner, a very long detector 24 is not required inorder to establish the same large component sensing envelope or field31. However, sequencing of sources 12, 14 is essentially the same as inthe previous embodiment.

FIG. 4 is an example of a double edged measurement as considered withrespect to sources 12, 14, since shadows of two edges of component 18fall on each of detectors 24A, 24B.

FIG. 5 is a diagrammatic illustration of component measurement system 60in accordance with another embodiment of the present invention. System60 bears many similarities to system 50, shown in FIG. 4, and likecomponents are numbered similarly. The main distinction between systems60 and 50 is the relative orientations of detector portions 24A and 24B.Specifically, referring to FIG. 4, faces of detector portions 24A and24B lie in approximately the same plane, and when viewed in twodimensions, appear co-linear. However, system 60, shown in FIG. 5,illustrates detector portions 24A and 24B disposed such that theprincipal axes of detector portions 24A and 24B do not lie in the sameplane. Thus, detector portions 24A and 24B of system 60 do not appearco-linear with respect to each other. Instead, detector portions 24A and24B are disposed normal to a centerline of illumination from therespective source for each detector portion. For example, detectorportion 24A appears to be oriented relative to source 14 such that ends62 and 64 are equidistant from source 14. Detector portion 24A is alsodisposed in the plane of shadow 20, and source sequencing operates asshown in the relative timing diagram in FIG. 5. Although detectorportions 24A and 24B are shown disposed at a relatively slight anglewith respect to each other, any suitable angle such as ninety degreescan be used.

FIG. 5 is an example of a double sided measurement, as considered withrespect to each source, since shadows of two edges of component 18 fallon each of detectors 24A, 24B.

FIG. 6 is a diagrammatic view of component measurement and detectionsystem 70 in accordance with another embodiment of the presentinvention. System 70 is similar to the embodiment shown in FIG. 2 andlike elements are numbered similarly. The main distinction betweensystems 70 and 10, in FIGS. 6 and 2 respectively, is the provision ofspecular reflective surfaces 72, 74. As can be seen, sources 12, 14direct their illumination away from detector 24 initially, whichillumination falls upon specular reflectors 72, 74, (typicallysubstantially specular) respectively, and is directed toward nozzle 30and detector 34. This embodiment allows for flexibility in placement ofsources 12, 14. Detector 24, as shown in FIG. 6, could also incorporateeither of the detector layouts shown in FIG. 4 or 5. However, inembodiments using split detector portions, and specular reflectors, itis contemplated that one source could utilize a specular reflector whileanother source could be positioned so that its principal ray is directlyincident upon the component, and thus not require a specular reflector.Further, although FIG. 6 illustrates the use of specular reflectorsbetween sources 12, 14 and the component, such specular reflectors couldbe disposed between the component and detector 34.

FIG. 7 is a diagrammatic view of component measurement and detectionsystem 80 in accordance with an embodiment of the present invention.System 80 is illustrated to show how embodiments of the presentinvention can be used to detect component offset and rotationalorientation for oversized components (e.g. single edge measurements).This discussion is provided to detail computation of rotational andpositional (x, y) offsets for single edge measurements, and can beextended to double sided measurements. U.S. Pat. No. 5,559,727 to Deleyalso provides for computation of rotational and positional offsets fordouble-sided measurements with a different light source/detectorarrangement, and is hereby incorporated by reference herein. FIG. 7shows an example of a single sided measurement with respect to either ofsources 12, 14, since only one shadow of an edge falls on each ofdetectors 24A, 24B. Such components are generally too large to fitshadows of opposite sides simultaneously upon any single detectorportion.

FIG. 7 illustrates component 100 casting shadows upon detector portions24A and 24B. However, each detector portion only captures a singleshadow, because component 100 is so large that the shadows of itsopposite sides do not fall upon detector portions 24A and 24B. In thisembodiment, detector outputs 28A and 28B are monitored while component100 is rotated in order to detect shadow minimums indicating whenrespective sides of component 100 are aligned with the a given rayemanating from either of sources 12, 14. For example, in the exampleshown in FIG. 7, slight clockwise rotation will bring edge 102 ofcomponent 100 into alignment with a ray emanating from source 14. Suchalignment will generate a local minimum upon detector portion 24A.Although in FIG. 7 it appears that the detectors are positioned at rightangles to the sources, it will be understood that non-orthogonalpositioning may also be employed.

To determine the x-axis and y-axis offset, the width of the component,the length of all of the sides of the component, and the rotationaloffset of the component in FIG. 7, consider the analogous example of onesource-detector pair of FIG. 7 shown in FIG. 8. The length of theminimum width is measured by finding the distance, D₁, between shadowedge and detector point O₁. The distance D₁ is related to componentdimension L₁ in the following manner.When the distance D1 is at a minimum: $\begin{matrix}\begin{matrix}{{\tan( {\alpha_{1}{\_ side}{\_ a}} )} = {\frac{L_{a}}{B_{1}} = \frac{D_{1} \cdot {\cos( {\phi_{1} - 90^{{^\circ}}} )}}{A_{1}}}} \\{so}\end{matrix} & {{Equation}\quad 1} \\\begin{matrix}{L_{a} = {\frac{B_{1}}{A_{1}}( {D_{1} \cdot {\cos( {\phi_{1} - 90^{{^\circ}}} )}} )}} \\{and}\end{matrix} & {{Equation}\quad 2} \\{{\alpha_{1}{\_ side}{\_ a}} = {\arctan( \frac{D_{1} \cdot {\cos( {\phi_{1} - 90^{{^\circ}}} )}}{A_{1}} )}} & {{Equation}\quad 3}\end{matrix}$

Equations for L_(c) and α_(1—)side_a can be derived similarly whenside_c is rotated to a similar position as side_a in FIG. 8. The encoderand encoder electronics captures the encoder rotation, E₁, the D₁ is atits minimum. If the step size between successive encoder rotations is T,then the part rotation encoder value when side_a is aligned to areference axis of the pick and place machine is perpendicular to a majoraxis of detector 24 b, is: $\begin{matrix}{E_{{aligned\_ side}{\_ a}} = {E_{1} + \frac{\phi_{1} - {\alpha_{1}{\_ side}{\_ a}}}{T}}} & {{Equation}\quad 4}\end{matrix}$Where α_(1—)side_a is the angle formed at point source 12 between theline to O₁ on detector 24 b and the line to S₁, and θ₁ is the angleformed at source 12 between the line to O₁ on detector 24 b and areference axis in the pick and place machine. The width of thecomponent, W_(ac), can be calculated as:W _(ac) =L _(a) +L _(c)  Equation 5And the offset of the nozzle axis 30 (the axis of rotation) from thecenter of the part along the line W is given by: $\begin{matrix}{F_{a\quad c} = \frac{L_{c} - L_{a}}{2}} & {{Equation}\quad 6}\end{matrix}$

The computation process described mathematically by Equations 1-6 can beoptionally repeated for the remaining two opposing sides of component100, from which orthogonal width and offset can be computed. Thisprocess can be iteratively applied to the component 100, where thevalues L_(a), L_(b), L_(c), L_(d), (length of sides of component 100)can be derived from any sequence of available minimums cast by sources12, 14 upon detectors 24 b, 24 a as determined by the sequencing ofenergizing of sources 12, 14 and the rotation of the component 100 withrespect to these sources.

FIG. 9 is a diagrammatic view of a component orientation and placementdetection system 210 in accordance with an aspect of the presentinvention. FIG. 9 is somewhat similar to FIG. 1, and like components arenumbered similarly. System 210 includes sources 212, 214 which arearranged to direct illumination 216 upon component 218 from at least twodifferent angles. Sources 212, 214 can be any suitable light sources aslong as they provide illumination of sufficient intensity as consideredfrom each source. Thus, sources 212, 214 can be incoherent or coherentillumination sources. Preferably, source 212, 214 are laser diodes, butin some embodiments, sources 212, 214 are light emitting diodes. Sources212, 214 can be positioned to provide illumination in substantially thesame plane, as defined by either of the sources and two points on thedetector (a beginning and an ending pixel on the detector).

Divergent illumination from sources 212, 214 passes through opticalelement 217 which functions to reduce the degree of divergence of theillumination, and preferably substantially collimate, light passingtherethrough. As illustrated, illumination passing through element 217from source 212 forms a first beam 219 having a reduced divergence,while that from source 214 forms a second beam 221 having a reduceddivergence. Preferably, optical element 217 is a lens that can be eitherspherical or cylindrical. However, a cylindrical lens is preferred. Theillumination emerging from element 217 is less divergent, providing amore compact ray bundle than would otherwise be present, therebyspeeding computation of component alignment, since less componentrotation is required. Additionally, those skilled in the art willrecognize that optical element 217 is disposed backwards from theoptically ideal orientation. In this manner, element 217 provides a flatsurface proximate the sensing field 223. The provision of a flat surfaceby element 217 proximate the sensing field provides a convenient seal insystem 210 against contaminants.

In accordance with one aspect of the present invention, filter 225 isdisposed proximate detector 224 in order to reduce ambient light fallingon detector 224. Filter 225 can filter based on incident light angles,and/or wavelengths.

Those skilled in the art will recognize that for a four-sided component,complete component measurement can be effected in about 225 degrees ofrotation (180 degrees to image both edges+45 degrees maximum to imagethe first edge). This is significantly faster than requiring a completecomponent rotation.

In some cases, the pick-and-place machine may not have any a prioriknowledge of component size. In such cases, the machine can perform a“source scan” where a plurality of sources are sequentially energized todetermine if any of the sources are disposed relative to the componentto cast at least one shadow portion on at least one detector. If suchcombination is found, component measurement and alignment can beperformed with the selected detector/source combination(s).

Operation of embodiments of the present invention generally involve thefollowing steps. The first step is calibrating the source, nozzle anddetector positions with respect to each other. There are a number oftechniques that can be employed for this operation. For example,calculation of the positions of the various sensor components can beperformed by placing the sensor with test components fixed in positionin a coordinate measuring machine and then using the coordinatemeasuring machine to identify the relative position of all of the testcomponents such that the position of the ray that is incident from thelight source or sources onto the detector is known with respect to thenozzle position and detector position.

As a second step, the shadow or shadows from each component cast uponthe detector by light incident from the source or sources has acharacteristic intensity profile that is processed to extract an edge.The edge position can be interpolated to subpixel position. Suchinterpolation can be effected using any number of techniques includingcentroid calculation or curve fitting. This, then, relates a particularedge position to an encoder position and a known source ray position.Then, the defined edge of the shadow provides an (r, θ) pair where θ isthe position of the encoder that is on the nozzle shaft or attached tothe nozzle shaft indicating its relative angular position, and (r, θ) isthe distance from the source to the edge position on the detector thatdefines the position of the component at that specific point in angularspace and time. The (r, θ) pairs are collected during the rotation ofthe component on the nozzle. These (r, θ) pairs are used to derive,using known geometric techniques as per FIG. 7 (r, θ, B₁) where θ isused with α to calculate angular part orientation, component informationincluding: component width, component length, nozzle off-set of rotationcenter x, nozzle off-set of rotation center y, and the angular positionof a defined frame of reference of the component with respect to thenozzle angular position. With this information, the component locationcan be translated into the specific pick and place machine's frame ofmechanical reference via software and the component can be properlypositioned to be placed upon its target location on the printed circuitboard.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. For example, multiple portions of detector24 could be placed within the same plane or without the same plane.Further, such detector portions need not be physically adjacent but maybe segments of detectors such that the multiple nozzles' position withrespect to the light sources and detectors allow components to be imagedon such detector portions based upon selection of sources that areturned on with respect to components and detector portions.

1. A sensor system for computing placement information about a componentin an electronic component handling machine, the machine releasablyholding the component and adapted to rotate the component, the sensorsystem comprising: a sensor; a plurality of divergent light sources inthe sensor disposed to illuminate a sensing field in the sensor; adetector positioned relative to the light sources so that when thecomponent is at least partially disposed in the sensing field, thecomponent blocks at least some illumination from at least one of theplurality of divergent light sources to form a shadow of at least aportion of the component on the detector, the detector adapted toprovide a plurality of detector outputs while the component rotates;optics interposed between a sensing field and the plurality of divergentlight sources to reduce the divergence of light passing therethrough;and computing electronics receiving the detector outputs to compute theplacement information.
 2. The sensor system of claim 1 wherein theoptics is a spherical lens.
 3. The sensor system of claim 2 wherein thespherical lens has a substantially flat surface disposed proximate thesensing field.
 4. The sensor system of claim 3 wherein the flat surfaceprovides a seal against contaminants.
 5. The sensor system of claim 1wherein the optics is a cylindrical lens.
 6. The sensor system of claim5 wherein the cylindrical lens has a substantially flat rear surface. 7.The sensor system of claim 6 wherein the substantially flat rear surfaceis disposed proximate the sensing field to provide a seal againstcontaminants.
 8. The sensor system of claim 1, wherein the opticssubstantially collimates light passing therethrough.
 9. The sensorsystem of claim 1, and further comprising an ambient light filterdisposed proximate the detector to reduce ambient light falling on thedetector.
 10. The sensor system of claim 9, wherein the filter is anangular filter.
 11. The sensor system of claim 9, wherein the filter isconfigured to pass the illumination wavelengths, but attenuate ambientlight.
 12. The sensor system of claim 11, wherein the filter is also anangular filter.